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Molecular Interactions of the Mammalian Intermediate Filament Protein Synemin with Cytoskeletal Proteins Present in Adhesion Sites Ning Sun Iowa State University

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Molecular Interactions of the Mammalian Intermediate Filament Protein Synemin with Cytoskeletal Proteins Present in Adhesion Sites Ning Sun Iowa State University Iowa State University Capstones, Theses and Retrospective Theses and Dissertations Dissertations 2008 Molecular interactions of the mammalian intermediate filament protein synemin with cytoskeletal proteins present in adhesion sites Ning Sun Iowa State University Follow this and additional works at: https://lib.dr.iastate.edu/rtd Part of the Molecular Biology Commons Recommended Citation Sun, Ning, "Molecular interactions of the mammalian intermediate filament protein synemin with cytoskeletal proteins present in adhesion sites" (2008). Retrospective Theses and Dissertations. 15814. https://lib.dr.iastate.edu/rtd/15814 This Dissertation is brought to you for free and open access by the Iowa State University Capstones, Theses and Dissertations at Iowa State University Digital Repository. It has been accepted for inclusion in Retrospective Theses and Dissertations by an authorized administrator of Iowa State University Digital Repository. For more information, please contact [email protected]. Molecular interactions of the mammalian intermediate filament protein synemin with cytoskeletal proteins present in adhesion sites by Ning Sun A dissertation submitted to the graduate faculty in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Major: Molecular, Cellular, and Developmental Biology Program of Study Committee Richard M. Robson, Major Professor Ted W. Huiatt Steven M. Lonergan Jo Anne Powell-Coffman Linda Ambrosio Iowa State University Ames, Iowa 2008 Copyright © Ning Sun, 2008. All rights reserved. 3316170 3316170 2008 ii TABLE OF CONTENTS ABSTRACT IV GENERAL INTRODUCTION 1 Dissertation Organization 1 Introduction 1 Review of Literature 3 References 14 HUMAN α-SYNEMIN INTERACTS DIRECTLY WITH VINCULIN AND METAVINCULIN 23 SYNOPSIS 23 INTRODUCTION 24 MATERIALS and METHODS 26 RESULTS 30 DISCUSSION 37 ACKNOWLEDGEMENTS 39 REFERENCES 40 IDENTIFICATION OF A REPEATED DOMAIN WITHIN MAMMALIAN α-SYNEMINTHAT INTERACTS DIRECTLY WITH TALIN 55 Abstract 55 Introduction 56 Materials and methods 57 Results 60 Discussion 65 Acknowledgements 67 References 67 SYNEMIN INTERACTS WITH THE LIM DOMAIN PROTEIN ZYXIN AND IS iii ESSENTIAL FOR CELL ADHESION AND MIGRATION 79 Abstract 79 Introduction 80 Materials and Methods 82 Results 87 Discussion 94 Acknowledgments 96 References 97 GENERAL CONCLUSIONS 110 CONPREHENSIVE LIST OF REFERENCES 113 ACKOWLEGEMENTS 125 iv ABSTRACT The type VI intermediate filament (IF) protein synemin is a very large, unique member of the IF protein superfamily. Synemin associates with the major type III IF protein desmin and/or vimentin forming heteropolymeric intermediate filaments (IFs) within mammalian muscle cells. Previous studies in our lab showed that avian synemin interacts with vinculin and α-actinin, both of which are cytoskeletal proteins present in adhesion sites such as the focal adhesions within cells. Thus, synemin may link the heteropolymeric IFs to adhesion sites within mammalian muscle cells or within some non-muscle cells that express synemin. At least two isoforms of synemin, namely α- and β-synemin, are present in mammals. The larger α-synemin is identical with the smaller β-synemin, with the only exception being that the slightly smaller β-synemin lacks a 312 amino acid insert (SNTIII) near the end of the long C-terminal tail domain. Whether the two mammalian synemin isoforms have different functions is unclear. Studies in this dissertation provide evidence that the two large mammalian (human) synemin isoforms interact differentially with several cytoskeletal proteins and thereby may fulfill different cellular functions. Mapping the binding site(s) of human synemins within vinculin and talin by in vitro protein-protein interaction assays revealed that SNTIII, which is absent in β-synemin, interacts specifically with both vinculin and talin. Transient expression of enhanced green fluorescent protein (EGFP)-tagged SNTIII co-localized with vinculin and talin at focal adhesion sites within mammalian cells. Confocal microscope analysis of intracellular localizations of endogenous synemin and vinculin/talin indicated that synemin co-localized with vinculin and talin at the sites of costameres, which are considered specialized focal adhesions located periodically along and immediately subjacent to the sarcolemma of mammalian striated muscle cells. These results indicated that mammalian α-synemin, but not β-synemin, interacts directly with the cytoskeletal proteins vinculin and talin within mammalian cells. To elucidate the possible functions of, and to identify novel interacting proteins for, the smaller β-synemin within cells, yeast two-hybrid screening of a human adult skeletal muscle cDNA library was performed using the entire tail domain of human β-synemin (SNβΤ) as the bait. The LIM domain protein zyxin was identified as an interaction partner of β-synemin. The interaction was further confirmed by v several in vitro protein-protein interaction assays. Furthermore, over-expression of the zyxin-binding region of synemin within mammalian cells blocked the localizations of endogenous zyxin to the focal adhesions without disrupting normal cellular architectures. Knockdown synemin expression within cells by siRNA resulted in significantly compromised cell adhesion and migration. These results in toto indicate that mammalian (human) synemin isoforms participate in the focal adhesion dynamics and are essential for cell adhesion and cell motility. 1 GENERAL INTRODUCTION Dissertation Organization The manuscript-based format is used in my dissertation with the inclusion of three papers. The main body consists of one paper published in Biochemical Journal, a second paper published in Experimental Cell Research, and a third manuscript that will be submitted for publication in the journal Molecular Biology of the Cell. I was responsible for the design, implementation, and interpretation of almost all of the experiments in these three papers. I did receive initial help and guidance from Rahul Bhosle, a previous graduate student in our lab, and from Dr. Susan Veneziano, a postdoctoral assistant in the lab. Dr. Denise Paulin and Dr. Zhenlin Li at the University of Paris provided the full-length human synemin cDNAs used in my research. The references cited in the literature review are in the format of author/year style for ease of reading. Those references cited in the manuscripts are formatted in the styles according to the requirements of each journal and are listed in separate Reference sections corresponding with each manuscript. A comprehensive list of references with article titles is included at the end of the dissertation following the GENERAL CONCLUSIONS section. Introduction The overall goal of the research described in this dissertation was to increase our understanding of the cellular functions of the two large isoforms of the mammalian type VI intermediate filament (IF) protein synemin. It is generally known that the ~310 amino acid conserved central rod domain of cytoplasmic IF proteins mediates IF protein assembly by forming “coiled-coil” structures, whereas the head and tail domains of IF proteins contain most of the binding sites for non-IF protein partners. Thus, the unusually large C-terminal tails (933 amino acids in β-synemin and 1245 amino acids in α-synemin) of the mammalian (human) synemins likely contain most of the binding sites for their non-IF protein partners. Indeed, previous studies in our lab demonstrated that the long C-terminal tail domain of avian synemin, which is expressed as only one form, was shown to interact with α-actinin and 2 vinculin. Avian synemin shares only ~35% sequence identity and ~53% sequence homology with the human synemin isoforms. Whether either of the two human synemin isoforms interact with vinculin has not been known. Furthermore, whether either synemin isoform interacts with metavinculin, which is a muscle specific isoform of vinculin, has also been unknown. The first manuscript (published in Biochemical Journal) included in this dissertation describes molecular interaction studies of the human α- and β- synemin isoforms with vinculin and metavinculin. The results demonstrate that the 312 amino acid insert (SNTIII), which is present only within α-synemin, interacts specifically with both vinculin and metavinculin, whereas regions from human β-synemin do not. Uyama et al. (2006, Gut 55:1276-1289) recently reported that synemin co-precipitates and co-localizes with talin, which is another key cytoskeletal protein regulating focal adhesion dynamics. However, information demonstrating direct interaction of synemin with talin has been unclear. The second manuscript (published in Experimental Cell Research) included in this dissertation demonstrates that SNTIII present in α-synemin, but not in human β-synemin, interacts specifically with the talin rod domain. Furthermore, SNTIII was found to be composed of seven ~39 amino acid tandem repeats. These studies in toto demonstrate that it is the human α-synemin isoform that interacts with vinculin and talin, thereby exhibiting functions not present within the smaller β-synemin isoform. To increase our understanding of the role(s) of the smaller β-synemin, yeast two-hybrid screening of a human adult skeletal muscle cDNA library, using the entire tail domain of human β-synemin as the bait, was performed. These studies are described in the third manuscript included in this dissertation. The protein zyxin, an adhesion plaque protein, was discovered to be a novel interaction partner for both human
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